CAPE CANAVERAL, Fla — NASA's Artemis 1 mission will open a new era of U.S. space exploration when it launches to the moon this month, but exactly when it lifts off depends on several factors.
Artemis 1, the first uncrewed test flight of NASA's Artemis program to return astronauts to the moon, is currently scheduled to lift off from Pad 39B of the Kennedy Space Center in Cape Canaveral on Saturday (Sept. 3) Liftoff is currently scheduled for 2:17 p.m. EDT (1817 GMT), weather permitting. You can watch the launch live online on Saturday starting at 12:15 p.m. EDT (1615 GMT), courtesy of NASA TV.
Artemis 1 has a 2-hour launch window
NASA has stressed repeatedly that Artemis 1 is, at its core, a test flight. It is the first-ever flight of the agency's new megarocket, the towering Space Launch System (SLS), as well as the first deep-space flight for the new Orion spacecraft. There may be technical glitches that come up during the launch countdown that warrant a delay.
"The test fight itself carries inherent risk," Jim Free, NASA associate administrator for exploration systems development, said in an Aug. 22 news conference. "This is the first flight of a new rocket and a new spacecraft."
In fact, an engine cooling issue forced NASA to call off an attempted launch on Aug. 29. The Sept. 2 launch attempt is the second of three NASA can make in its current window.
NASA has a two-hour window in which to launch Artemis 1 on Sept. 3. That means the launch could occur anytime between 2:17 p.m. and 4:17 p.m. EDT (1817-2017 GMT), although NASA is targeting the start of the window.
Weather could also cause a delay. Currently, there is a 60% chance of good weather at launch time, according to an Aug. 31 forecast (opens in new tab) from the Space Launch Delta 45 weather group at Cape Canaveral Space Force Station. The primary concerns are thick clouds, surface electrical fields from lightning and the possibility the SLS may have to fly through rain on its ascent. The weather group will issue daily weather updates through launch. You can find those on the Space Launch Delta 45 website (opens in new tab).
What if Artemis 1 doesn't launch ontime?
If technical issues or bad weather delay the Artemis 1 mission, NASA does have some options.
Originally, the mission was scheduled to launch on Monday, Aug. 29, at 8:33 a.m. EDT (1233 GMT), with two initial backup launch days in Artemis 1's current flight window: Friday, Sept. 2 and Monday, Sept. 5. Both dates have their own extended launch windows. In fact, there are launch opportunities on Sept. 2, Sept. 3, Sept. 4 and Sept. 5, but only if NASA doesn't fuel the rocket fully on the first of those attempts.
Because of the engine cooling issue, NASA was forced to delay the launch. But instead of targeting Sept. 2, the agency opted to target the Sept. 3 launch window on Saturday. That launch date has a two-hour window to get off the ground. That target still allows for a longer mission of between 38 and 42 days, NASA has said in a flight date calendar.
If NASA is unable to launch on Sept. 3, its last chance is Sept. 5. That's because it will take 48 hours to replenish the supply of liquid hydrogen propellant the SLS rocket needs for launch, NASA officials said last week.
The Sept. 5 launch date calls for a liftoff at 5:12 p.m. EDT (2212 GMT). The launch window for this date is a bit shorter, 90 minutes as opposed to two hours, but does allow NASA to pursue a longer 42-day flight. Landing would occur on Oct. 17.
What if NASA misses this Artemis 1 launch window?
If NASA is unable to launch the Artemis 1 mission during the Aug. 29 to Sept. 5 period, the agency would have to fall back on a series of additional launch windows that run throughout the rest of the year and early 2023.
In May, the space agency unveiled a calendar of launch opportunities through mid-2023 that met a series of criteria needed for the Artemis 1 mission. That list was updated earlier this month as NASA weighed possible launch options.
Here's a look at when those additional launch opportunities could occur.
- Sept. 19-Oct. 4, except for Sept. 29-30;
- Oct. 17-Oct. 31, except for Oct. 24-26 and Oct. 28;
- Nov. 12-Nov. 27, except for Nov. 20-21 and Nov. 26 (preliminary);
- Dec. 9-23, except for Dec. 10, 14, 18 and 23 (preliminary).
You can download NASA's full Artemis 1 launch availability calendar (opens in new tab) (PDF) to see how the dates stack up.
How does NASA pick Artemis 1 launch dates?
NASA has four primary requirements that drive how it selects launch dates for Artemis 1. Here's what they are, according to a NASA data sheet (opens in new tab).
- The moon's position in its orbit: The moon's location dictates the launch day because NASA wants to place Artemis 1 in what's called a "distant retrograde orbit" around the moon. To do that, the SLS current upper stage has to perform a maneuver called a trans-lunar injection burn at a specific point, with respect to the moon's position, to put it on the right course.
- Orion's lighting conditions: NASA mission rules dictate that the Orion spacecraft cannot be in darkness for more than 90 minutes at a time. This is because Orion is solar powered, so it needs sunlight on its arrays, and also to maintain its optimum temperature.
- Orion's "skip" reentry plan: In order to pinpoint Orion's splashdown location in the Pacific Ocean, NASA wants to try a "skip" reentry in which the space capsule dips into the Earth's upper atmosphere, then skips out briefly before making its final reentry. To do that, it has to launch during certain windows to reach the right trajectory upon its return to Earth, NASA says.
- Orion's splashdown lighting conditions: NASA wants Orion to splash down during the daytime hours to make it easer for recovery teams to spot the capsule and retrieve it out of the ocean.
All of those requirements make for a complicated calculus when it comes to determining a launch date for Artemis 1.
If you're planning to watch NASA's Artemis 1 launch online, Space.com will carry the agency's webcast live on Saturday (Sept. 3). A fueling webcast will begin at 5:45 a.m. EDT (0945 GMT), with the launch webcast beginning in earnest at 12:15 a.m. EDT (1615 GMT).
NASA is also expected to livestream several post-launch events, including a press conference, confirmation of the trans-lunar injection maneuver and the first views of Earth from the Orion spacecraft. You can see a full schedule in our Artemis 1 webcast guide.
Editor's note: This story was updated on Sept. 1 with NASA's new launch target dates and times for the Artemis 1 mission after its delay on Aug. 29.